The size of passenger cars manufactured in the United States have decreased in the past few years. Most of the size decrease has been through a reduction in the size of the luggage trunk. An even further size reduction in passenger cars is anticipated within the next decade which could essentially eliminate the trunk as a place for the transportation of luggage. Since a majority of vehicle owners have become accustomed to traveling distances which require overnight stops, it has been suggested that small cargo trailers could offer a solution to the transportation of luggage. However, before such cargo trailers are generally accepted by most people, it is imparative that stability be maintained between the towing vehicle and the trailer, especially when traveling above 50 miles per hour.
One form of instability exhibited by tow vehicle-trailer combinations currently available is trailer sway which causes the trailer to oscillate in a manner similar to the movement of a pendulum. This instability often causes severe yawing in the trailer which can lead to loss of steering control of the tow vehicle. With an anticipated weight reduction of future vehicles resulting from a decrease in size, the loss of steering control from such instability could be accelerated.
To alleviate such sway instability, some trailers have been equipped with dampening devices attached to the hitches such as: the shock absorbers located on opposite sides of the hitch as disclosed in U.S. Pat. No. 3,722,920; and the friction disc arrangement disclosed in U.S. Pat. No. 3,785,680. These anti-sway devices operate sufficiently as long as the tow vehicle-trailer is moving in a straight line. However, when it is desired to turn the tow vehicle-trailer combination, the tow vehicle must overcome the resistance of the anti-sway devices.
In an effort to overcome the turning resistance of anti-sway devices, a power cylinder disclosed in U.S. Pat. No. 3,834,480 is operationally responsive to the fluid in a power steering system for allowing the trailer to track the tow vehicle during turning operations.
As the size of the trailer was increased to accommodate more cargo, it became evident that the brake system in the tow vehicle would be insufficient to stop this tow vehicle-trailer within the safety standards set by the Department of Transportation in the United States. Thus, it became evident that an independent brake system would be needed for the trailer. One such trailer brake system disclosed in U.S. Pat. No. 3,880,263 uses the input force developed between a ball-tongue coupling of the tow vehicle and trailer to operate a pressure producing means which provides the fluid pressure to effect a brake application in the trailer. This type of trailer brake system is completely acceptable for most two wheel trailers. Unfortunately, as the size of vehicles is reduced, the ability to carry a portion of the load of the trailer by the tow vehicle is proportionally reduced.
In an effort to use the same size trailer, it has been suggested in U.S. patent application Ser. No. 921,918 that a nose wheel be added to the tongue of the trailer. The nose wheel is connected to and steerable by the tow vehicle, however, all the braking of the tow vehicle trailer combination is dependent on the brake system in the tow vehicle.